(a) List five classes of food other than carbohydrates. (b) Explain why glucose is taken by an athlete ready for a race rather than corn meal. (c) Describe ...

(a) Five classes of food other than carbohydrates

1. Proteins
2. Fats and oils (lipids)
3. Vitamins
4. Mineral salts
5. Water

(Roughage/dietary fibre is also accepted as a class.)

(b) Why glucose rather than corn meal is taken by an athlete ready for a race

Glucose is a simple sugar (monosaccharide) that requires no digestion. It is absorbed directly and quickly through the wall of the small intestine into the blood, so it provides instant energy for the race. Corn meal, on the other hand, is a complex carbohydrate (starch) that must first be digested (broken down by enzymes into glucose) before it can be absorbed. This digestion takes time, so the energy from corn meal is released too slowly to be useful for an athlete about to run.

(c) Test for starch

1. Place a small quantity of the food sample on a white tile or in a test tube.
2. Add a few drops of iodine solution to the sample.
3. Observation: the iodine changes from brown/yellow to a blue-black colour.
4. Conclusion: the blue-black colour confirms that starch is present. (If the colour remains brown, starch is absent.)